1. Field of the Invention
The present invention relates generally to nuclear power plants and, more particularly, to a method of operating a nuclear power plant at multiple power levels during the course of a fuel cycle.
2. Description of the Related Art
The design and operation of nuclear power plants in the United States are highly regulated. The federal regulations regarding the licensing of nuclear power plants are set forth at 10 C.F.R. xc2xa7 50. In applying for a license on a nuclear power plant from the Nuclear Regulatory Commission (NRC), one must set forth various operating parameters of the power plant, including the thermal power level at which the reactor will be operated and above which the reactor will not be permitted to be operated. In determining what will be the operating power of a nuclear reactor for purposes of obtaining a license, one must perform calculations that assume multiple simultaneous worst-case scenarios, even though many of such scenarios cannot, as a practical matter, exist simultaneously. As a general matter, therefore, power ratings of nuclear reactors in the United States are conservative with respect to the actual power capacity of such reactors.
As an additional matter, such calculations typically assume that certain conditions within the reactor are at their worst-case values, i.e., maximum or minimum values, at all times during the course of a fuel cycle of the reactor, when in fact such values can vary in a known fashion from the beginning of cycle to the end. Accordingly, such nuclear reactors operate at power levels below what could be achieved if the values of such conditions were considered as being variable and not fixed at their worst case levels.
Two examples of such variable values of reactor conditions are the heat flux peaking factor (FQ) and the enthalpy rise peaking factor (Fxcex94H). It is known that FQ is typically at a maximum at the beginning of a fuel cycle and decreases with the depletion of the fuel rods of the reactor. It is also known that Fxcex94H typically starts at an initial value and increases slightly in the initial stages of a fuel cycle but thereafter decreases with depletion of the fuel rods. Calculations that are performed in order to determine a power level at which a reactor will be licensed to operate are based on the assumption that the values of FQ and Fxcex94H are fixed at their maximum levels, although such values are at a maximum for only a relatively short period of time during the fuel cycle.
A nuclear power plant is generally said to comprise a reactor and the Balance Of Plant (BOP), with the BOP including all of the apparatus that interacts with the reactor in order to generate electricity. It is also known that the various components of the BOP are designed to operate at a given operating level, but typically include an additional margin, whether as a factor of safety, a design excess in order to comply with rating requirements, or for other reasons. It is also known that various environmental factors can affect the performance of a nuclear power plant. For instance, a cooling tower may be designed to have a certain rated capacity at 80xc2x0 F. and 90% relative humidity, and may be designed with a margin of an additional 2%. Accordingly, the cooling tower can operate at another 2% above its rated capacity at 80xc2x0 F. and 90% relative humidity. On a winter day with a temperature of 20xc2x0 F. and 10% relative humidity, however, the cooling tower may be operating at only 90% of its rated capacity to meet the cooling needs of the power plant. Accordingly, on such a winter day the cooling tower potentially could provide an additional 12% capacity. It thus can be seen that the performance conditions of the various components of the BOP, as well as the process parameters of the environment, can cause the BOP to have an additional aggregate capacity above and beyond what is needed when the reactor is operating at its rated power level. It thus would be desirable to take advantage of the excess capacity of the BOP, perhaps in conjunction with reductions in FQ and Fxcex94H below their maximum values with the depletion of the fuel rods.
Accordingly, a method of operating a nuclear power plant includes determining and licensing a maximum power level at which the power plant can be operated subsequent to the beginning of a fuel cycle, and with the power plant being operated at less than its maximum power rating at certain times such as at the beginning of a fuel cycle. The maximum power level is greater than the power level that would be calculated based upon an assumption that the heat flux peaking factor (FQ) and enthalpy rise peaking factor (Fxcex94H) remain at their maximum level throughout an entire fuel cycle. The maximum power rating takes advantage of factors such as known reductions in FQ and Fxcex94H at certain points in the fuel cycle, the marginal additional capacity of the Balance Of Plant, and the occasional optimization of process parameters such as ultimate heat sink temperature and atmospheric conditions. The power plant may be operated at a substantially continuously variable power level based upon various factors of the power plant, but would not exceed the NRC licensed core thermal power level.
We provide a method of operating a nuclear power plant through a fuel cycle by operating the plant at an initial power level during a first portion of the fuel cycle, and by operating the plant at an enhanced power level during a second portion of the fuel cycle. The initial power level typically will be based upon the maximum values of FQ and Fxcex94H that are calculated for a given reactor core configuration. The enhanced power level is higher than the initial power level and is based at least in part upon the known fact that FQ generally decreases throughout a fuel cycle and that the Fxcex94H reaches a maximum in the beginning stages of the fuel cycle but thereafter decreases with depletion of the fuel rods. Formulas set forth below describe a manner in which the FQ and Fxcex94H can be calculated. Other formulas set forth a manner in which reduced values of FQ and Fxcex94H at which the power plant can be operated at an enhanced power level are calculated.
The enhanced power level may be determined, at least in part, upon a maximum power level. The maximum power level may, at least in part, be based upon an assumption that at least one performance condition of the plant is at a maximum level and/or that at least one process parameter of the plant or its environment is in an optimum condition. The enhanced power level may vary between the initial power level and the maximum power level depending upon prevailing performance conditions and process parameters.
The enhanced power level may be a substantially continuously variable power level in which the power level at any given moment is based at least in part upon a corresponding FQ and/or a corresponding Fxcex94H.
One method in accordance with the present invention of operating a nuclear power plant through a fuel cycle of a core of a reactor of the plant, with the core including a plurality of fuel rods in communication with a plurality of channels, and with a coolant flowing through the channels, can be generally stated as including operating the plant at an initial power level during a first portion of the fuel cycle, the initial power level being based at least in part upon at least one of a maximum value of a heat flux peaking factor of the core and a maximum value of an enthalpy rise peaking factor of the core, and operating the plant at an enhanced power level during a second portion of the fuel cycle, the enhanced power level being higher than the initial power level, the enhanced power level being based at least in part upon at least one of a reduced value of the heat flux peaking factor of the core and a reduced value of the enthalpy rise peaking factor of the core. The reduced values of the heat flux peaking factor and the enthalpy rise peaking factor result from the progressive depletion of the core during the fuel cycle.
Another method in accordance with the present invention operating a nuclear power plant through a fuel cycle of a core of a reactor of the plant, with the core including a plurality of fuel rods, can be generally stated as including determining an initial power level based at least in part upon at least a first design limitation of the plant and at least one of a maximum value of a heat flux peaking factor of the core and a maximum value of an enthalpy rise peaking factor of the core, determining a maximum power level based at least in part upon at least one of an assumption that at least a first performance condition of the plant is at a maximum level and an assumption that at least a first process parameter is at an optimum condition, the maximum power level being greater than the initial power level, determining a reduced value of the heat flux peaking factor of the core based upon the maximum value of the heat flux peaking factor, the initial power level, and the maximum power level, determining a reduced value of the enthalpy rise peaking factor of the core based upon the maximum value of the enthalpy rise peaking factor, the initial power level, and the maximum power level, determining the one of the heat flux peaking factor and the enthalpy rise peaking factor that will achieve chronologically last the reduced value of the heat flux peaking factor and the reduced value of the enthalpy rise peaking factor, respectively, during the fuel cycle, operating the plant at the initial power level during a first portion of the fuel cycle, determining the one of the heat flux peaking factor and the enthalpy rise peaking factor of the core, and operating the plant at an enhanced power level between the initial and maximum power levels during a second portion of the fuel cycle upon the one of the heat flux peaking factor and the enthalpy rise peaking factor achieving the reduced value of the heat flux peaking factor and the reduced value of the enthalpy rise peaking factor, respectively. The reduced values of the heat flux peaking factor and the enthalpy rise peaking factor result from the progressive depletion of the core during the fuel cycle.
Another method in accordance with the present invention of operating a nuclear power plant through a fuel cycle of a core of a reactor of the plant can be generally stated as including determining a maximum power level for the reactor, obtaining a license to operate the reactor at the maximum power level, operating the reactor at an initial power level less than the maximum power level during a first part of the fuel cycle, and operating the reactor at an enhanced power level during a second part of the cycle, the enhanced power level being between the initial power level and the maximum power level, with the increase in power level from the initial level to the enhanced power level being based at least in part upon the progressive depletion of the core during the fuel cycle.